JP5612221B2 - Sleep clock error recovery scheme - Google Patents

Description

  [0001] The present invention relates to wireless communications, and more particularly, to a more stable low power oscillator design.

  [0002] Bluetooth (registered trademark) is a wireless protocol for exchanging data over a short distance (using short-length radio waves) from a fixed device and a mobile device. Bluetooth is intended for low-power applications, often in devices such as fax machines, mobile phones, telephones, laptops, personal computers, printers, global positioning system (GPS) receivers, digital cameras, and video game consoles used. Bluetooth uses a radio technology called frequency hopping spread spectrum, which divides the data being sent and transmits these chunks of data over up to 79 bands of 1 MHz width in the range 2402-2480 MHz. .

  [0003] The Bluetooth wireless link is formed in the context of a piconet. A piconet comprises two or more devices that occupy the same physical channel (this means they are synchronized to a common clock and hopping sequence). The common (piconet) clock is identical to the Bluetooth clock of one of the devices in the piconet, known as the piconet master, and the hopping sequence is derived from the master clock and the master Bluetooth device address. All other synchronized devices are called slaves in the piconet.

  [0004] Bluetooth is a packet-based protocol having a master / slave structure. One master can communicate with up to seven slaves in the piconet, and all devices share the master's clock. Packet switching is based on a basic clock defined by the master, which ticks at 312.5 μs intervals. Two clock ticks create a slot of 625 μs, and two slots create a slot pair of 1250 μs. In the simple case of a single slot packet, the master transmits in even slots and receives in odd slots, and conversely, the slave receives in even slots and transmits in odd slots. Packets can be 1 slot long, 3 slots long or 5 slots long, but in all cases, master transmission starts with even slots and slave transmission starts with odd slots.

  [0005] The Bluetooth specification includes a low power mode called sniff mode, which may be more generally referred to as a low power sleep mode, or simply a sleep mode for simplicity. In sniff mode, devices that are not actively communicating may enter a low power (sleep) state while periodically sending “keep alive” messages or transmissions to each other. In other words, in the sniff mode, the transmitter device and the receiver device that have established the communication link periodically communicate with each other to maintain the link. For example, if the user is using a Bluetooth keyboard or mouse and has not provided input for a period of time, the keyboard or mouse will enter a low power sniff mode and the Bluetooth master device The (host computer) will periodically communicate with the slave device (keyboard or mouse) to maintain the link. Sniff mode provides the greatest benefit to battery-operated human interface devices and also provides increased battery life for these devices.

  [0006] The Bluetooth specification requires that the Bluetooth device maintain a 3.2 kHz Bluetooth clock even during sleep. During sleep, Bluetooth requires that the clock be maintained within 250 ppm +/− 10 μs. If the device includes an internal low power oscillator (LPO), the internal LPO circuit may create clocks that sometimes drift over 250 ppm. This drift is due to noise, temperature changes, supply voltage fluctuations, or a combination of the above.

  [0007] In the case where the Bluetooth device clock drifts beyond 250 ppm, the two devices may have difficulty maintaining a communication link during sniff mode. This is due to the difference in clock between the master device and the slave device, and the master may send a sniff message while the slave device is in the sleep state. In the case of a slave device in a sniff link, this slave device can open its scan window so that it can find the master transmitter. The slave device can typically open its window by the desired amount to allow an acceptable clock drift error range of 250 ppm on either side of the link.

  [0008] However, even in the case where the slave device increases its scan window, the master device may still send a sniff communication when the slave device is in sleep mode. For example, the master cannot assume that the slave will open its receive window beyond +/− 250 ppm, nor can it request the slave to do so. The master device must perform the master transmission on time (as determined by the clock) and at the appropriate frequency, otherwise the link will receive a link monitoring timeout (during this timeout). There may be a negotiated or programmable number of attempts to revive the link).

  [0009] Other corresponding problems associated with the prior art will become apparent to those skilled in the art after comparing such prior art to the embodiments described herein.

  [0010] Embodiments of the invention relate to maintaining a communication link between devices in a wireless communication system, such as, for example, a Bluetooth system. A wireless communication system includes a master device and one or more slave devices. When the slave device enters a low power mode (or sleep mode), the master device periodically sends keep alive messages to the slave device to maintain the communication link. In some embodiments, the master device is configured to determine the amount of time since the last successful keepalive transmission was sent to the slave device. The master device then determines an appropriate number of keepalive transmissions and an appropriate transmission time for the keepalive transmissions based on the determined amount of time since the last keepalive transmission. sell. The master device may then send multiple keep alive messages at scheduled times to maintain the communication link.

[0011] The objects, features and advantages of the present invention may be more fully understood by reference to the following detailed description when read in conjunction with the accompanying drawings.
FIG. 1 shows a Bluetooth system that includes an exemplary Bluetooth device. FIG. 2 is a block diagram of a Bluetooth master transmitter device, according to one embodiment. FIG. 3 is a flowchart diagram of a method for recovering from a sleep clock error, according to one embodiment. FIG. 4 illustrates a chart of temporal relationships for sleep mode transmission between a master wireless device and a slave device, according to one embodiment. FIG. 5 illustrates an example timing diagram for planned sleep mode transmission between a master wireless device and a slave device, according to one embodiment. FIG. 6 illustrates an example timing diagram for actual sleep mode transmission between a master wireless device and a slave device, according to one embodiment. FIG. 7 is a flowchart diagram of a method for recovering from a sleep clock error according to one embodiment.

  [0019] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. However, the drawings and detailed description thereto are not intended to limit the invention to the particular forms disclosed, but on the contrary, the intent is that of the invention as defined by the appended claims. It is to be understood that this is to cover all modifications, equivalents, and alternatives included within the spirit and scope. It should be noted that headings are used for organizational purposes only and are not intended to be used to limit or interpret the description or the claims. Further, throughout this application, the term “may be” is used in a sense of acceptance (ie, is possible or possible) and has a mandatory meaning ( Note that it is not a must. The term “include” and its derivatives mean “including but not limited to”. The term “coupled” means “directly or indirectly connected”.

  [0020] Embodiments of the invention described herein include a "sleep mode" to maintain a communication link between two devices, and at least one of the two devices is in a low power mode It can be used in any of various wireless communication systems that utilize messages sent between two devices that can be placed. Embodiments are described below in the context of a Bluetooth system. As used herein, the term “Bluetooth” refers to the Bluetooth wireless communication standard and includes past, present and future versions of this standard. It should also be noted here that the following embodiments are exemplary and the embodiments may be applied to other similar types of systems. Further, the terms “sleep mode” and “sleep frame” correspond to, or are used herein generically, the Bluetooth-specific terms “sniff mode” and “sniff frame”, respectively. Please note that. In addition, as used herein, the term “keep-alive transmission” or “keep-alive message” corresponds to the Bluetooth-specific term “sniff packet” or is used to generically refer to this term. The

  [0021] FIG. 1 illustrates an example wireless communication system, according to one embodiment. The illustrative system of FIG. 1 is a Bluetooth system. This illustrative system includes a computer system 102 that can operate as a Bluetooth transmitter / receiver, or transceiver, that can be configured to implement embodiments of the present invention. The computer system 102 includes various standard components, such as at least one processor and memory, a display, and various other hardware / software, just as the computer system standard is. The computer system 102 includes a Bluetooth transmit / receive device, ie, a transceiver device (200 in FIG. 2) configured to operate as described herein.

  [0022] The computer system 102 communicates with one or more peripheral devices, such as a Bluetooth keyboard 112, a Bluetooth mouse 114, and / or a Bluetooth headset 116, as shown. Each peripheral device 112, 114, 116 may be a battery (or other portable energy source) device that communicates wirelessly with the host computer 102.

  [0023] Any of various types of computer systems, in particular smartphones or other mobile phones, microphones, speakers, digital cameras, light pens, joysticks, fax machines, printers, global positioning system (GPS) reception Other types of wireless devices are also contemplated such as machines, personal digital assistants (PDAs), digital audio and / or video players, and video game consoles. In some embodiments, instead of or in addition to a processor and memory, the wireless device may have some other type of functional, eg, ASIC (application specific integrated circuit), field programmable gate array. Note further that programmable hardware elements such as (FPGA) may be utilized. As used herein, the term “functional unit” refers to a component (or components) that comprises hardware and / or software and is capable of performing a specific function.

  [0024] As described above, FIG. 1 is merely an example, and embodiments may operate with any of various combinations of devices that communicate with each other in a wireless manner.

  [0025] FIG. 2 is a block diagram of an exemplary Bluetooth master transceiver device 200 that may be included in any of the Bluetooth devices shown in FIG. The Bluetooth master transceiver device 200 may be configured to operate as a master transmitter (or transceiver) device. As shown, the Bluetooth device 200 can comprise a functional unit, such as, for example, a processor 202 coupled to a memory 204, although other types of functional units can be used as desired, For example, a programmable hardware element such as a field programmable gate array (FPGA), ASIC (application specific integrated circuit), etc., as desired. The Bluetooth device 200 also includes an antenna 206 and various Bluetooth circuits 208 for implementing Bluetooth communication including a clock 210, such as a low power oscillator. It should be noted that in other embodiments, the clock can be implemented in any of a variety of ways and can be located elsewhere in the device.

  [0026] The memory 204 may store various types of program instructions for operation of the Bluetooth device 200. As shown, memory 204 may also store error recovery program instructions 212. Error recovery program instructions 212 may be executed by processor 202 to perform embodiments of the methods and functions described herein, eg, the methods and functions described in the flowcharts and timing diagrams of FIGS. It can be. Alternatively, the error recovery functions disclosed herein may be implemented in hardware as desired, eg, through appropriately configured programmable hardware, eg, FPGA, or other logic, or in software and hardware. Can be implemented in combination. More generally, the error recovery function can be implemented via a functional unit.

  FIG. 3 is a flowchart illustrating the operation of one embodiment of a method for recovering from a clock error. This method may be performed by a Bluetooth device operating as a master transmitter, such as computer system 102. The master wireless device can enter a sleep mode (302), eg, a sniff mode for a Bluetooth embodiment. The master wireless device is wirelessly coupled to at least one slave wireless device that is also in sleep mode. The master and slave wireless devices have determined that, for example, at least one slave wireless device is idle and enters sleep mode (ie, low power sleep mode, or sniff mode) to conserve battery power Can enter sleep mode. For example, if the slave wireless device is a Bluetooth keyboard and the user has not entered any input on the keyboard for a predetermined amount of time (no key on the keyboard pressed) The Bluetooth keyboard can enter sleep (eg, sniff) mode.

  [0028] The master wireless device determines an amount of time since the last successful keepalive transmission with at least one slave wireless device (304). In some embodiments, success is defined as receipt of an acknowledgment following transmission. In some embodiments, the passage of a specified amount of time since the detection of the last keep-alive transmission triggers the action illustrated in blocks 306-308 described below. The master wireless device determines (306) the number of keepalive frames to send to the slave wireless device and the appropriate time and frequency channel to send the keepalive transmission. In some embodiments, the number of keep-alive frames is multiple. In some embodiments, the master wireless device transmits the number of keepalive transmissions to the slave wireless device based on the amount of time since the last keepalive transmission, as determined at block 304. To decide.

  [0029] In determining the number of keep-alive transmissions to transmit to the slave wireless device in block 306, the master wireless device may examine the data structure as shown in the table of FIG. 4 described below. The master wireless device may also determine an appropriate transmission time for the keep alive frame by examining the data structure. The data structure can be stored in error recovery program instructions 212 in memory 204. The master device starts transmission of the selected number of keep-alive frames (308). The operations performed in blocks 306-308 can be repeated in response to repeated failures to detect transmissions from slave devices, and in some embodiments, for various iterations. The transmission times can be differently spaced in response to the state at each repetition time. In addition, some embodiments may provide an expected or predicted clock drift rate to recalculate the number and interval of transmissions in response to repeated execution of the operations described above for blocks 306-308. Can be adjusted.

  [0030] FIG. 4 illustrates a chart of temporal relationships for sleep mode transmission (keep alive transmission) between a master wireless device and a slave device, according to one embodiment. Table 400 shows a series of values used to determine if the probability of successful clock recovery is high when sending multiple sets of keepalive packets (or sniff frames) at 1.25 millisecond intervals. (Reflects). Table 400 shows a slot period of 625 microseconds. For each table entry 402-414, the number of slots is shown in the slot column 416. For each table entry 402-414, a time column 418 indicates the amount of time for the number of 625 microsecond slots shown in the slot column 416.

  [0031] For each table entry 402-414, an error column 420 indicates the magnitude of the error indicated by the predicted clock drift error range or allowed error tolerance. In the case of table 400, a 250 ppm tolerance of the predicted clock drift error rate is shown in error column 420. Error column 420 shows the amount of error resulting from a crystal with an error of 250 ppm for a selected number of slots in the slot column 416 of entries. If the LPO frequency is mistuned with an error of 250 ppm, the amount listed in error column 420 is the expected or predicted clock drift. Error column 420 is calculated by multiplying time column 418 by an acceptable error fraction (eg, clock drift rate), which in the case of table 400 is the time column for entry 402. The value of 12.5 milliseconds for 420 would be multiplied by 250 and divided by 1 million to produce a value of 3.125 microseconds in error sequence 420.

  [0032] Error frame sequence 422 represents a conversion from the errors listed in error sequence 420 to a corresponding number of Bluetooth transmission frames. The frame is composed of two slots. As described above, the slot period is 625 microseconds. Thus, each frame is 1.25 milliseconds. Bluetooth devices keep time in slots and frames. For example, a sniff interval is typically represented by a frame or slot. For example, the sniff interval may be calculated as 20 slots (or 160, or 320). Each entry 402 provides the number of potential drift frames in the error frame sequence 422 for a given sniff interval in the slot sequence 416. The value in the slot column 416 can be thought of as a synch period that represents how many slots have passed since the last contact with the slave device.

  [0033] Table 400 demonstrates that as the sniff period increases, the potential length of time associated with the error represents an increasing number of frames. Determining the relationship between the sniff period and the length of potential time associated with the error can be sent to increase the probability of interaction with the slave device (sniff packet) Allows the number of times to be determined. Given the belief that the LPO is 250 ppm accurate, then an uncertainty of approximately +/− 2 frames will appear after the 16000 slot period. In some embodiments, if the device determines that a possible error in the LPO frequency can be as high as, for example, 1000 ppm, the value in this column can be multiplied by 4 and 16000 Over the slot period gives an uncertainty of approximately +/− 8 frames. The number of master transmissions sent can then be determined as a reflection of the represented error.

  [0034] FIG. 5 illustrates an example timing diagram for a planned keep-alive transmission between a master wireless device and a slave device, according to one embodiment. FIG. 5 includes a master timeline 500 and a slave timeline 502. Master timeline 500 includes a series of transmit windows 504-512 and receive windows 514-522. Slave timeline 502 includes a transmission window 524 and a reception window 526.

  In the example depicted in FIG. 5, the master clock encounters an error and places the master timeline 500 at a time that is 400 ppm offset from the slave timeline 502. In order to restore the communication link between the master device and the slave device, the master determines that the master device will transmit a maximum of 5 keep-alive transmissions in the transmission window 504-512. The master device's Bluetooth Resource Manager (BRM) wakes up the master system two slots earlier than normal, eg, wakes in the transmit window 504 and adjusts the frame count by two so that the Bluetooth circuit can keep-alive transmit. Request to generate. If no response from the slave device is received, the BRM again adjusts the frame count to the sleep time position and retransmits in the transmit window 506. In the example described above, the transmission is approximately -1000 ppm (transmission window 504), -500 ppm (transmission window 506), on-time (transmission window 508), +500 ppm (transmission window 510), and +1000 ppm (transmission). In window 512) it is planned to be performed up to 5 times. In the example of FIG. 5, the slave clock is 400 ppm off the master clock, so the fourth transmission in the transmission window 510 arrives at the slave reception window 526 and is answered by the slave transmission 524, which is the master reception window. Received at 520.

  [0036] Once a sleep response is found, the master can adjust its clock to be the clock that is creating the sniff transmission to which the slave responded, and the link can continue. Adjusting the master clock embodies the assumption that the master clock is in error and modifies the master clock by adjusting the master clock to match the slave clock. However, even if the error is in the slave clock, resynchronization to the slave clock will provide benefits for many applications. Embodiments help to increase the likelihood that the link will be maintained because the clock has been realigned. A synchronous link, such as a synchronous connection oriented (SCO) link, that can be affected in such a case, has no response during a relatively long time period and is time sensitive during sleep. Used in embodiments that tend to not actively send time-sensitive synchronization data. In some embodiments, sleep transmissions in transmission window 504-512 are treated as priority frames. If transmission is pre-empted by other Bluetooth or WALN traffic (via a coexistence interface), the subsequent sleep period also uses sleep recovery if no sleep response is found Will.

  [0037] As an alternative to sending keep-alive transmissions in every frame, the transmitter may transmit in several frame periods in one sleep anchor and then in other sleep periods in another sleep anchor. Optionally, it can be selected. For example, the transmitter may choose to send with an even frame offset (-4, -2, 0, 2, 4) in one sleep anchor and then send with an odd frame offset in the next anchor. Such an embodiment can be selected to save power and is useful if the device exceeds 5 seconds without a sleep response because the slave opens the window longer than an entire frame period. It can be proven. Such an embodiment is also useful if the master has other Bluetooth traffic to transmit or if the WLAN traffic on the coexistence interface requires a medium for some traffic. Can be proved.

  [0038] While one of ordinary skill in the art would have read the present disclosure, while the transmission depicted in FIG. 5 is aligned to correspond to frame boundaries, some embodiments are described in this document. It will be understood that transmission across frame boundaries is included by adjusting the clock resolution in increments of a few hundred microseconds without departing from the scope of the disclosure. In addition, while the illustrative embodiments disclosed herein have been described for a single master and a single slave for simplicity, those of ordinary skill in the art should have read this disclosure. In light of this, it will be appreciated that embodiments supporting multiple slaves may be implemented without departing from the scope of the present disclosure. Solutions for adapting multiple sniff links may include support for recovery for only a single link in multiple master / slave relationships. Furthermore, some embodiments implement multiple master clocks for multiple slave links.

  [0039] FIG. 6 illustrates an exemplary results timing diagram for the planned time diagram shown in FIG. FIG. 6 includes a master timeline 600 and a slave timeline 602. Master timeline 600 includes a series of transmit windows 604-610 and receive windows 614-620. Slave timeline 602 includes a transmission window 624 and a reception window 626.

  [0040] In the example depicted in FIG. 6, the master clock encounters an error that causes the master timeline 600 to produce a 400 ppm offset relative to the slave timeline 602. To restore the communication link between the master device and the slave device, the master plans to send a maximum of 5 sleep transmissions in the send window 604-610, although only 4 are actually sent. . The BRM of the master device wakes up the master system two slots earlier than normal, for example, in the transmission window 604, adjusts the frame count by 2 and requests that the Bluetooth circuit generate a sleep transmission. If no response from the slave is received, the BRM again adjusts the frame count to the sleep time position and retransmits in the transmit window 606. In the example described above, this is approximately -1000 ppm (transmit window 604), -500 ppm (transmit window 606), on-time (transmit window 608), +500 ppm (transmit window 510), and +1000 ppm (not shown by cancellation). Is planned to be performed up to 5 times. In this example, the slave clock is 400 ppm different from the master clock, so the fourth transmission in transmit window 510 arrives at slave receive window 626 and is answered by slave transmit 624, which is the master receive window 620. Received at.

  [0041] Once a sleep response is found, the master can adjust its clock to the slave clock, as reflected in the adjusted time value 628, and the link can continue. The assumption embodied thereby is that the master clock is in error, and the master clock is modified by adjusting to the slave clock.

  [0042] FIG. 7 is a flowchart diagram of a method for recovering from a sleep clock error, according to one embodiment. This method may be performed by a Bluetooth device operating as a master transmitter, such as computer system 102. The master wireless device may enter a sleep mode (702), eg, a sniff mode for a Bluetooth embodiment. The master wireless device is wirelessly coupled to at least one slave wireless device that is also in sleep mode. The master and slave wireless devices have determined that, for example, at least one slave wireless device is idle and enters sleep mode (ie, low power sleep mode, or sniff mode) to conserve battery power Can enter sleep mode. For example, if the slave wireless device is a Bluetooth keyboard and the user has not entered any input on the keyboard for a predetermined amount of time (no key on the keyboard pressed) The Bluetooth keyboard can enter sleep (eg, sniff) mode.

  [0043] The master wireless device determines an amount of time since the last successful keep-alive transmission with at least one slave wireless device (704). In some embodiments, success is defined as receipt of an acknowledgment following transmission. The master wireless device determines the number of sleep frames to send to the slave wireless device and the appropriate time to send multiple keep-alive transmissions (706). In addition, in some embodiments, the appropriate channel frequency is determined. In some embodiments, the number of sleep frames is multiple. In some embodiments, the master wireless device transmits the number of keep-alive transmissions to send to the slave wireless device based on the amount of time since the last keep-alive transmission, as determined at block 704. Can be determined.

  [0044] In determining the number of keep-alive transmissions to be transmitted to the 706 slave wireless devices, the master wireless device may examine the data structure as shown in the table of FIG. 4 described above. The master wireless device may also determine an appropriate transmission time for the sleep frame by examining the data structure. The master wireless device may also consider the amount of time remaining before link monitoring timeout in some embodiments. In such an embodiment, more aggressive transmission of multiple sniff frames may be appropriate as a response to the link monitoring timeout approach. The data structure can be stored in error recovery program instructions 212 in memory 204. Thereafter, the master device transmits a sleep frame, also called keep-alive transmission (708).

  [0045] A determination is made as to whether a slave response has been received (710). If a slave response is received, the master clock is adjusted (712). If no slave response is received, a determination is made as to whether the connection has timed out (714). If the connection times out, the connection is terminated (716). If the connection has not timed out, processing returns to block 708, which has been described above.

[0046] Although the above embodiments have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. The following claims should be construed to include all such variations and modifications.
Hereinafter, the invention described in the scope of claims of the present application will be appended.
[C1] A wireless device,
A functional unit;
A radio transceiver and an antenna coupled to the functional unit;
A clock coupled to the functional unit and the wireless transceiver and configured to generate a clock signal;
With
The wireless device is wirelessly coupled to at least one wireless slave device, and the functional unit is:
a) determining an amount of time since the last keep-alive transmission with the at least one slave device based on the clock;
b) based on the determined amount of time from the last successful keep-alive transmission, the number of keep-alive transmissions sent to the at least one slave device and the time of the next scheduled keep-alive transmission. Determine an appropriate transmission time for the keep-alive transmission;
c) starting continuous transmission of the number of keep-alive transmissions to the at least one slave device for each determined transmission time;
Configured as a wireless device.
[C2] The functional unit further includes:
Determine an appropriate frequency channel for the keep-alive transmission;
Responsive to the at least one slave device receiving at least one of the number of keep-alive transmissions, receiving a keep-alive transmission from the at least one slave device;
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do not send the rest,
The wireless device according to C1, configured as follows.
[C3] The functional unit further includes:
Adjusting the clock based on the received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
The wireless device according to C1, configured as follows.
[C4] In order to determine the number of keep-alive transmissions to transmit, the functional unit
Further determining the number of keep-alive transmissions and an appropriate transmission time based further on an estimated clock drift error rate;
The wireless device according to C1, configured as follows.
[C5] The functional unit is configured to perform a) to c) in response to failing to detect a keep-alive transmission from the at least one slave device for a specified amount of time. The wireless device according to C1, wherein:
[C6] The functional unit further includes:
In response to each failure to detect keep-alive transmissions from the at least one slave device for the specified amount of time, each time a plurality of iterations of a) to c) are performed. Note that the appropriate transmission time for at least two of the plurality of repetitions is different.
The wireless device according to C5, configured as follows.
[C7] The functional unit further includes:
increasing the predicted clock drift rate in response to failing to detect a keep-alive transmission from the at least one slave device after performing a) to c) a specified number of times;
The wireless device according to C1, configured as follows.
[C8] The wireless device according to C1, wherein each transmission of the keep-alive transmission for the number of times is performed on a boundary of a transmission frame.
[C9] The functional unit is
A processor;
A memory coupled to the processor;
The wireless device according to C1, comprising:
[C10] The functional unit includes one or more functional units.
Programmable hardware elements, or
Application specific integrated circuit (ASIC),
The wireless device according to C1, comprising:
[C11] A method for recovering from a sleep clock error,
The wireless master device determines, based on the clock, an amount of time since the last keep-alive transmission for the wireless connection to the at least one slave device;
Based on the determined amount of time from the last successful keepalive transmission, the number of keepalive transmissions to be transmitted to the at least one slave device and the keep time for the next scheduled keepalive transmission. Determining an appropriate transmission time for an alive transmission;
Starting a continuous transmission of the number of keep-alive transmissions to the at least one slave device at each determined transmission time;
A method comprising:
[C12] determining an appropriate frequency channel for the keep-alive transmission;
Receiving the keep-alive transmission from the at least one slave device in response to the at least one slave device receiving at least one of the number of keep-alive transmissions;
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do n’t send the rest,
The method of C11, further comprising:
[C13] adjusting the clock based on the received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
The method of C11, further comprising:
[C14] The determination of C11, wherein determining the number of keep-alive transmissions to transmit further comprises determining the number of keep-alive transmissions and an appropriate transmission time based on an estimated clock drift error rate. the method of.
[C15] The method according to C11, wherein each transmission of the number of keep-alive transmissions is performed on a transmission frame boundary.
[C16] A non-transitory computer readable storage medium that stores program instructions that, when executed, cause one or more computers to implement the method, the method comprising:
The wireless master device determines, based on the clock, an amount of time since the last keep-alive transmission for the wireless connection to the at least one slave device;
Based on the determined amount of time since the last keep-alive transmission, the number of keep-alive transmissions to be transmitted to the at least one slave device and the keep-alive transmission with respect to the next scheduled keep-alive transmission time. Determining an appropriate transmission time for
Starting continuous transmission of the number of keep-alive transmissions to the at least one slave device for each determined transmission time;
A non-transitory computer-readable storage medium comprising:
[C17] The method further comprises:
The at least one slave device receiving a keep alive transmission from the at least one slave device in response to receiving at least one of the number of keep alive transmissions;
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do n’t send the rest,
A non-transitory computer-readable storage medium according to C16, comprising:
[C18] The method further comprises:
Adjusting the clock based on the received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
A non-transitory computer-readable storage medium according to C16, comprising:
[C19] The C16 described in C16, wherein determining the number of keep-alive transmissions to transmit further comprises determining the number of keep-alive transmissions and an appropriate transmission time based on an estimated clock drift error rate. Non-transitory computer-readable storage medium.
[C20] The non-transitory computer-readable storage medium according to C16, wherein each transmission of the number of keep-alive transmissions is performed on a boundary of a transmission frame.

Claims (17)

A wireless device,
A functional unit;
A radio transceiver and an antenna coupled to the functional unit;
A clock coupled to the functional unit and the wireless transceiver and configured to generate a clock signal;
With
The wireless device is wirelessly coupled to at least one wireless slave device, and the functional unit is:
Based on the a) said clock, determines the amount of time it last keep-alive transmission successful has elapsed since been carried out with the at least one slave device,
b) is the determination of the keep-alive transmissions the last successful, based on the amount the time that has elapsed, the number of keep-alive transmission to be transmitted to the at least one slave device, then scheduled keep-alive transmission wherein determining the transmit time for the keep-alive transmissions for time,
c) starting continuous transmission of the number of keep-alive transmissions to the at least one slave device for each determined transmission time;
Is configured to,
The functional unit further comprises:
Adjusting an error of the clock based on a received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
Configured as a wireless device. The functional unit further comprises:
Determining the frequency channel for the keep-alive transmission,
Wherein the at least one slave device in response to receiving at least one of a keep-alive transmission of the number of times to receive the keep-alive transmission from the at least one slave device,
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do not send the rest,
The wireless device of claim 1, configured as follows. In order to determine the number of keep-alive transmissions to transmit, the functional unit
Further based on the predicted clock drift error rate, it determines the keep-alive transmission times and transmit time,
The wireless device of claim 1, configured as follows. The functional unit, between the amount during the specified time, in response to failure to detect the keep-alive transmissions from the at least one slave device configured to perform a) to c), The wireless device according to claim 1. The functional unit further comprises:
Wherein between between amount when specified, in response to each of the failure to detect keepalive transmissions from said at least one slave device, each time, to perform multiple repetitions of a) to c) , At least two prior Kioku Shin time for one of said plurality of iterations, different,
The wireless device of claim 4 , configured as follows. The functional unit further comprises:
a) to c) after performing the specified number of, in response to failure to detect the keep-alive transmissions from the at least one slave device, to increase the predicted clock drift rate,
The wireless device of claim 1, configured as follows.   The wireless device according to claim 1, wherein each transmission of the number of keep-alive transmissions is performed on a transmission frame boundary. The functional unit is
A processor;
A memory coupled to the processor;
The wireless device of claim 1, comprising: The functional unit is one or more,
Programmable hardware elements, or application specific integrated circuits (ASICs),
The wireless device of claim 1, comprising: A method for recovering from a sleep clock error comprising:
And that the wireless master device, based on a clock, to determine the amount of time that the keep-alive transmission successful end to wireless connection to at least one slave device has elapsed since been made,
The last is the determination of the keep-alive transmission successful, based on the amount the time that has elapsed, the number of keep-alive transmission to be transmitted to the at least one slave device, then scheduled keep-alive transmission times and determining a transmit time for the keep-alive transmissions for,
Starting continuous transmission of the number of keep-alive transmissions to the at least one slave device for each determined transmission time;
Adjusting an error of the clock based on a received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
A method comprising: Determining a frequency channel for the keep-alive transmission,
Receiving the keep-alive transmission from the at least one slave device in response to the at least one slave device receiving at least one of the number of keep-alive transmissions;
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do n’t send the rest,
The method of claim 10 , further comprising: Wherein determining the number of keep-alive transmission to be transmitted, further comprising, based on the predicted clock drift error rate, determines the keep-alive transmission times and transmit time, according to claim 10 the method of. The method according to claim 10 , wherein each transmission of the number of keep-alive transmissions is performed on a transmission frame boundary. A non-transitory computer readable storage medium storing program instructions that, when executed, cause one or more computers to implement the method, the method comprising:
And that the wireless master device, based on a clock, to determine the amount of time that the keep-alive transmission successful end to wireless connection to at least one slave device has elapsed since been made,
The last is the determination of the keep-alive transmission successful, based on the amount the time that has elapsed, the number of keep-alive transmission to be transmitted to the at least one slave device, then scheduled keep-alive transmission times and determining a transmit time for the keep-alive transmissions for,
Starting continuous transmission of the number of keep-alive transmissions to the at least one slave device for each determined transmission time;
Adjusting an error of the clock based on a received keep-alive transmission from the at least one slave device, thereby synchronizing the clock to the at least one slave wireless device;
A non-transitory computer-readable storage medium comprising: The method further comprises:
Determining a frequency channel for the keep-alive transmission;
The at least one slave device receiving a keep alive transmission from the at least one slave device in response to receiving at least one of the number of keep alive transmissions;
In response to receiving the keep-alive transmission from the at least one slave device, the continuous transmission of the keep-alive transmission for the number of times is stopped, whereby any one of the keep-alive transmissions for the number of times Do n’t send the rest,
The non-transitory computer readable storage medium of claim 14 , comprising: Wherein determining the number of keep-alive transmission to be transmitted, further comprising, based on the predicted clock drift error rate, determines the keep-alive transmission times and transmit time, according to claim 14 Non-transitory computer-readable storage medium. The non-transitory computer-readable storage medium according to claim 14 , wherein each transmission of the number of keep-alive transmissions is performed on a transmission frame boundary.

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